SHOWER

The basic idea of electron identification is to measure electromagnetic showers produced in lead material. The HADES pre-shower detectors consist of 2 lead converters inserted between three wire chambers with pad read-out. Shower recognition is performed by comparing the number of particles measured before and after the lead converters. Particle hits are identified via charge produced in ionization processes in the wire chambers working in the self quenching streamer mode (SQS). The main advantage of the SQS mode is that induced charge is nearly independent of particle specific energy loss and therefore low energy protons do not produce large signals in the post converter chambers because of their significant energy loss in the lead material and finally are not misidentified with electromagnetic showers.